Reduced calorie fats which are made from triglycerides containing short or medium and long chain fatty acids have been disclosed for use as a replacement for conventional triglyceride fats in food products. See, for example, Seiden; U.S. Pat. No. 5,288,512; Issued Feb. 22, 1994 which discloses reduced calorie fat compositions comprising at least about 15% by weight triglycerides selected from the group MML, MLM, LLM, and LML triglycerides and mixtures thereof; wherein M=fatty acids selected from the group consisting of C.sub.6 to C.sub.10 saturated fatty acids, and mixtures thereof, and L=fatty acids selected from the group consisting of C.sub.17 to C.sub.26 saturated fatty acids, and mixtures thereof. See also Wheeler et al; U.S. Pat. No. 5,258,197; Issued Nov. 2, 1993, which discloses reduced calorie fat compositions containing at least about 25% by weight triglycerides selected from the group SSL, SLS, LLS, LSL and mixtures thereof; wherein S-fatty acids selected from the group consisting of C.sub.18 to C.sub.22 saturated fatty acid and mixtures thereof.
Reduced calorie triglycerides containing short or medium and long chain fatty acids can be prepared by a variety of techniques including the selective esterification of long chain fatty acid monoglycerides with short or medium chain fatty acids. See, for example, Kluesener et al; U.S. Pat. No. 5,142,071; Issued Aug. 25, 1993 which discloses a process for the selective esterification of long chain monoglycerides, particularly monobehenin, with medium chain fatty acids, particularly a mixture of C.sub.8 and C.sub.10 fatty acid. In this process, an at least about 60% pure C.sub.18 -C.sub.24 fatty acid monoglyceride, or mixture thereof, is esterified with an at least about 90% pure C.sub.6 -C.sub.10 fatty acid or mixture thereof at a temperature of from about 140.degree. C. to about 250.degree. C. in the substantial absence of an esterification catalyst. The mole ratio of fatty acid to monoglyceride used in this monoglyceride esterification is at least about 3:1.
Unfortunately, preparation of reduced calorie triglycerides containing short or medium chain and long chain fatty acids by esterification of monoglycerides with short or medium chain fatty acids can result in the formation of fatty acid anhydrides which can be converted to difatty ketones during purification of the reduced calorie triglycerides. As a result, reduced calorie triglycerides prepared according to this type of process can contain high levels of difatty ketones. For example, these reduced calorie triglycerides can contain up to about 1% (10,000 ppm) difatty ketones. Levels of difatty ketones OffTOm about 100 to about 1000 ppm are typical for these reduced calorie triglycerides. Difatty ketones are difficult to remove from the reduced calorie triglyceride and can contribute to flavor instability and formation of bloom in chocolate applications and can act as a crystal inhibitor.
It would therefore be desirable to provide a process for preparing reduced calorie triglycerides which contain short or medium and long chain fatty acids, but which nevertheless do not contain unacceptably high levels of difatty ketone. It has now been found that the level of difatty ketones present in the reduced calorie triglyceride can be reduced by up to 95% (e.g. to about 10-20 ppm) by adding a hydroxyl-containing compound, such as glycerine, to the crude reduced calorie triglyceride at some point during the preparation of the reduced calorie triglycerides described herein. Adding the hydroxyl-containing compound removes fatty acid anhydrides, and thereby prevents the formation of difatty ketones.